A system of this kind is known, for instance, from SE-B-468 441, where the building foundations beneath the floor define a space which can be referred to generally as a miniature cellar or crawl in space. This space is thermally insulated and is sufficiently large to accommodate service equipment such as heat exchangers, water heaters, water and sewage connections, and the like. Exhaust air is ducted from the building interior to a heat exchanger in the service space and then discharged as extract air from the foundations/the building to atmosphere through an outlet duct. Ambient or outdoor air is taken as supply air through an inlet duct and passed to a heat exchanger for heat exchange with the exhaust air, from where the supply air is passed to the service space. The supply air is then passed from the service space to the residential areas in the building, through a slot which extends around the perimeter of the external walls and the floor.
One problem with known foundations of this kind is that a heat exchanger is needed for the exchange of heat between the supply and the exhaust air. Another problem is that such heat exchangers must be cleaned regularly. Yet another problem with such known systems is that the circulation of air in the residential areas/the utility areas is determined by the flow of supply and exhaust air to and from the building. A further drawback is that the service space must be given a size which will enable the space to accommodate the heat exchanger or heat exchangers and to afford room for them to be cleaned. The service space must also be heavily insulated.